The present invention relates to a process for disintegration and pure-sorted separation of the different plastics of composite structural parts to be recycled as generally known, for example, from Japanese Patent Application of 21.06.1989 laid open under No. 077307/1991 on 31.01.1991, and more specifically, to parts containing a core of at least foam material and a flexible outer foil adhering firmly thereto and a support made thicker-walled than the outer foil and composed of a hard plastic, firmly adhered to the core in the form of an intermediate layer. Generally speaking, the present invention is directed to a process which includes the step of comminuting the composite structural parts into approximately cuboid particles comprising different plastics, disintegrating the particles into individual materials by selectively comminuting the foam of the particles mechanically into substantially smaller crumbs than the remaining pieces of the particles in a dry treatment and separating the particles in a pure-sorted manner by a grain-size-selective separation such that the smaller foam crumbs are screened off from the coarser remaining particle pieces. Selective comminution of the foam takes place by a impact stressing of the particles, and, after the removal of the foam fraction, the initially remaining mixture of thicker-walled hard-plastic particles and of thinner-walled foil chips is separated into a hard-plastic fraction and into a foil fraction by a vertical low-turbulence upwind sifter, an approximately vertically rising low-turbulence air stream flowing from below against the particles of the mixture which lie flat and individually without overlap, on an air-permeable approximately horizontal base, with only the foil chips being lifted and carried upwards, and the hard-plastic particles remaining being removed laterally at screen level.
In such plastic composite parts, which are used to a great extent in the interior fittings of motor vehicles, several problems arise as regards reusability. For example, the different materials are adhesively bonded with one another very firmly by foam and usually cannot be released from one another or not completely or clearly enough. However, the plastics cannot be reused as a material mixture, and therefore they can be deposited in unsorted form as refuse only at great expense and by causing environmental harm. Furthermore, as regards three-component composite structural parts having a support made of hard plastic, a foam intermediate layer and a foil as an outer skin, there is the further difficulty, where the hard-plastic particles and foil particles are concerned, that they have approximately the same specific gravity and cannot be separated by known separating processes. Even during the production of parts of this kind of composite alone, approximately 30% by weight occurs as stamping waste during the stamping out of perforations and during trimming and as occasional rejects. Moreover, the elimination of parts from old cars after they have been scrapped must also be considered. In view of the large amount of composite parts of this kind, therefore, the problem of how the materials could be removed from the refuse and nevertheless still be used as useful materials is desired to be solved in a way which can be implemented in practice.
The above-mentioned Japanese Preliminary Publication 077307/1991 describes a process for dividing and sorting the different plastics of composite structural parts, especially foil-covered foam parts, in which a coarse comminution in a granulation of 20 to 50 mm is first carried out. The heap of coarse particles is agitated intensively in a high-speed agitator unit having a propeller agitator which rotates in a plane lying horizontally and near the bottom of the agitating container. Shearing forces are exerted on the particles by the rotor blades of the agitator unit and the materials can be detached from one another. The longer the operation continues, the more detachment takes place. Depending on the plastic type of the plastics involved in the composite structural part, a varying fineness of the stock treated in this way is obtained. The ground stock is subsequently classified according to grain size, at least one fraction occurring in a sort purity suitable for reuse. On account of the varying wear resistance of the foam fraction, on the one hand, and of the remaining plastics, on the other hand, the foam material cannot only be finely crumbled by a mechanical fulling or agitation of the particle heap, but can also be rubbed off completely from the other plastic fragments in the region of the adhesive bond, so that these are left entirely free of foam. However, the known process is restricted only to two-component composite structural parts containing one foam component. Experience has demonstrated that the previously known process cannot be applied to all types of foam. Regardless of the type of foam, the known process also cannot be employed for all foam-containing composite structural parts which contain hard plastics reinforced by glass-fiber mats because these plastics, under a shearing or frictional stress on the particle heap, split up or delaminate into thinner sheet-like fragments which cannot be separated in a pure-sorted manner from foil chips of different material.
Furthermore, irrespective of the type of foam, foam-containing three-component composite structural parts having two different plastic components also cannot be separated in a pure-sorted manner in respect of the other two plastics by the known process, as long as the two plastics do not differ or differ only very slightly in terms of the usual classification criteria, such as absolute or specific weight or specific gravity or particle size, as happens in most cases.
U.S. Pat. No. 5,042,725 is also concerned with the problem of suitable treatment of composite structural parts of the type in question here to enable the individual materials to be reused. It describes a process which as a whole works under dry conditions and in which the composite structural parts are first granulated to approximately 10 mm and the particles are then sorted in a plurality of steps, specifically first according to grain size and thereafter according to weight. The weight sorting takes place on an apparently inclined vibrating table having an air-permeable table board through which air is blown upwards. The particles of higher mass collect on one longitudinal side of the table board and the parts of lower mass on the opposite side. An electrostatic charging of the foam particles is prevented or reduced by dampening or by spraying with an anti-static liquid.
It is assumed, of course, in the known process that the sorted-out smaller or lighter particles consist essentially of foam. The foam fraction obtained by the process described there is alleged to contain only approximately 2% by weight of foil in the foam and thus occur in reusable purity. The coarser or heavier fractions, for which no particular further processing is proposed, contain essentially the foil chips, but small pieces of foam apparently still adhere firmly to these, and they are consequently not obtained in the necessary purity for reuse. Other dividing and sorting processes for three-component composite structural parts are also mentioned, and these are likewise based on a granulation of the parts to be treated, but proceed with fundamentally different methods not relevant here. The process described in the above-mentioned U.S. patent is also restricted to only two-component composite structural parts with one foam component. Three-component composite structural parts having two further different plastic components also cannot be separated in a pure-sorted manner by this known process in respect of the other two plastics which are difficult to differentiate. Therefore, these plastics have to either be reused as a poor-grade mixture or disposed of, with all the adverse consequences in terms of cost and the environment.
EP-A 422,460 describes a process for dividing and sorting the different plastics of stamping waste from vehicle dashboards. Such waste occurs when installation orifices for instruments, radios, ventilation gratings or the like are stamped out. The stamping waste consists of a base layer of hydrophilic polyurethane foam and an outer skin of hydrophobic PVC foil connected thereto. The waste pieces are first comminuted into approximately 3 mm large cuboid particles and subsequently swirled in water in the ratio of granules to water of 1 to 7 by an agitator unit in order to separate and sort the different plastics, in the course of which the water-absorbing PU foam swells. The swelling foam detaches from the PVC foil which remains dimensionally stable. Inasmuch as foam particles detached from the foil particles cannot in any case, because of the residual gases still included, float up to the water surface automatically and be collected at a vessel overflow, a complete separation of the foam particles from the foil pieces can be brought about by a flotation operation. The foil pieces which have a substantially higher specific gravity than water can be collected on the bottom of the water vessel and pumped off at intervals. After a drying of the material particles separated in a pure-sorted manner, the materials can be reused.
It is questionable whether the above-described process leads at all to a practicable separation of the different plastic sorts in a reusable sort purity. In particular, in view of the elasticity and compressibility of the foam, the forces which can be exerted on the adhesive bond between the foam and foil as a result of a swelling of the foam residue on the particles are much too low to overcome the substantially higher adhesive forces in such a way that the foam residue can burst off from the foil chips. A detachment of the foam particles from the foil chips can be expected, at most, in regions of an extremely poor adhesive bond between foam and foil which are proportionately small and are not wanted or in the at most theoretically possible case of a subsequent adhesive bonding of a foam body and a formed outer skin by the use of a water-soluble adhesive. Moreover, this process is not workable with three-component composite structural parts having, in addition to foam fractions, also two further plastic components which, although different in terms of material, can nevertheless be differentiated with difficulty where conventional classifying processes ar concerned.
An object of the present invention is to improve the generally known process mentioned at the outset, such that three-component composite structural parts which have two plastic components, different in terms of material and differentiable with difficulty where conventional classifying processes have been concerned, can separate all the plastics involved in a sort purity which is practicable for reuse, without disposable mixed fractions of poor-grade or non-reusability being obtained and without causing variations on the useful materials which impair or make impossible their reusability.
Taking the known process as a starting point, the foregoing object has been achieved according to the present invention by, on one hand, the step of selective comminution of the foam by an impact stressing of the particles, and, after the removal of the foam fraction, the initially remaining mixture of thicker-walled hard-plastic particles and of thinner-walled foil chips is separated into a hard-plastic fraction and into a foil fraction by a vertical low-turbulence upwind sifter, an approximately vertically rising low-turbulence air stream flowing from below against the particles of the mixture which lie flat and individually without overlap, on an air-permeable approximately horizontal base, with only the foil chips being lifted and carried upwards, and the hard-plastic particles remaining being removed laterally at screen level.
Alternatively, the step of selective comminution of the foam can take place in accordance with the present invention by an impact stressing of the particles, and, after the removal of the foam fraction, the initially remaining mixture of thicker-walled hard-plastic particles and of thinner-walled foil chips is separated into a hard-plastic fraction and into a foil fraction by a vibrating-screen separation assisted by an upwardly directed air flow. A vibrating conveyor effect is exerted on the particles, which are dumped in a spread-out entangled state on a vibrating screen inclined relative to a horizontal line and a mesh width of which is markedly smaller than the particle size of the mixture, and is directed towards a higher edge of the vibrating screen. A bearing force of the particles on the vibrating screen and a drag force exerted on the particles as a result of friction relative to the screen are reduced by the upwardly directed air flow, such that the vibrating conveying effect exerted on the lighter foil chips is substantially lower than that on the hard-plastic particles, and only the hard-plastic particles are thereby conveyed to the higher edge of the vibrating screen, whereas the foil chips are discharged via a lower edge of the vibrating screen.
In the former process for carrying out the present invention, the initially remaining mixture of thick-walled hard-plastic fragments and thin-walled foil chips is separated in a pure-sorted manner by a vertical low-turbulence wind sifting which affords a high selectivity. In the latter solution for achieving the objects of the present invention, a procedure with a so-called air jig is used instead.
The advantages of the dividing and sorting process according to the present invention include:
1. A good mutual separation of the individual material fractions from the composite structure is achieved, i.e. the foil particles and the hard-plastic particles are completely free of foam. PA0 2. The individual non-foam particles survive the first treatment step unchanged and undamaged, so that they can still be sorted reliably. PA0 3. The particle mixture consisting of the individual material fractions can be sorted in a reusable purity such that each material is pure. PA0 4. It is possible to reuse the individual materials in an appropriate way usable only in highly sorted form. PA0 5. The amount of refuse is reduced. PA0 6. A commercially viable efficient process results in which components already proven elsewhere are employed. PA0 7. The parts to be treated remain dry during the entire process and can subsequently be reused directly, so that an energy-intensive drying can be avoided. PA0 8. The plastic foil involved and the hard plastic are treated with care and are comminuted into relatively coarse particles of a granulation of preferably approximately 10 to 20 mm which is important, especially with regard to fiber-reinforced hard plastics and their reusability because the included fibers can also be used in an appropriate way only when there is a coarse comminution of such materials; if there is a very fine granulation of fiber-reinforced plastics for the purpose of their reuse, the short fiber fragments act merely as a weighting filler.